Fluoride protects against dental caries primarily through local effects at the tooth surface, whereas enamel fluorosis is entirely of systemic origin. Epidemiologic data strongly suggest that, under some conditions, fluoride intake during infancy is a causative factor in development of fluorosis of the permanent teeth. Feedings for infants differ very widely with regard to fluoride content, ranging from breast milk with its extremely low fluoride content to powder formulas reconstituted with fluoridated water, which have fluoride concentrations in excess of 1000 mug/L. The following questions will be addressed: (1) What is the retention of fluoride resulting from the wide range of fluoride intakes provided by current infant feeding regimens? (2) Is fluoride absorbed less well from soy formulas than from milk-based formulas? These questions will be answered with the use of metabolic balance studies in normal infants. It is expected that the results will show that fluoride retention is proportional to fluoride intake and that fluoride retention will be much higher when powder formulas reconstituted with fluoridated water are fed than when ready-to-feed formulas are fed. Fluoride retention should be intermediate when concentrated liquid formulas are fed. Fluoride retention with all formulas will be higher than fluoride retention reported in the literature for breast-fed infants. The proposed research will obtain the data necessary for developing sound recommendations regarding fluoride intake by infants.